Adds a diff suppress function for the `engine_version` attribute of the `db_instance` AWS resource.
The function only supresses the state diff, if the attribute key `auto_minor_version_upgrade` is set, and if the returned `engine_version` from the running RDS instance shares the same prefix as the configured `engine_version`.
```
$ make testacc TEST=./builtin/providers/aws TESTARGS='-run=TestAccAWSDBInstance_MinorVersion'
==> Checking that code complies with gofmt requirements...
go generate $(go list ./... | grep -v /terraform/vendor/)
2017/01/23 17:59:14 Generated command/internal_plugin_list.go
TF_ACC=1 go test ./builtin/providers/aws -v -run=TestAccAWSDBInstance_MinorVersion -timeout 120m
=== RUN TestAccAWSDBInstance_MinorVersion
--- PASS: TestAccAWSDBInstance_MinorVersion (503.48s)
PASS
ok github.com/hashicorp/terraform/builtin/providers/aws 503.518s
```
This commit adds a new "attachment" style resource for setting the
policy of an AWS S3 bucket. This is desirable such that the ARN of the
bucket can be referenced in an IAM Policy Document.
In addition, we now suppress diffs on the (now-computed) policy in the
S3 bucket for structurally equivalent policies, which prevents flapping
because of whitespace and map ordering changes made by the S3 endpoint.